Add HttpClientFactory and update Graph client to use it

composer.json

@@ -13,7 +13,9 @@
 	],
 	"require": {
 		"php": "^8.0 || ^7.3",
-		"guzzlehttp/guzzle": "^6.0 || ^7.0",
+		"guzzlehttp/guzzle": "^7.0",
+		"php-http/httplug": "^2.2.0",
+		"php-http/guzzle7-adapter": "^1.0.0",
 		"ext-json": "*"
 	},
 	"require-dev": {

src/Core/NationalCloud.php

@@ -0,0 +1,53 @@
+<?php
+/**
+ * Copyright (c) Microsoft Corporation.  All Rights Reserved.
+ * Licensed under the MIT License.  See License in the project root
+ * for license information.
+ *
+ * HttpResponse File
+ * PHP version 7
+ *
+ * @category  Library
+ * @package   Microsoft.Graph
+ * @copyright 2020 Microsoft Corporation
+ * @license   https://opensource.org/licenses/MIT MIT License
+ * @version   GIT: 1.13.0
+ * @link      https://graph.microsoft.io/
+ */
+
+namespace Microsoft\Graph\Core;
+
+/**
+ * Class NationalCloud
+ * Defines Graph Hosts for the various national clouds
+ * @package Microsoft\Graph\Core
+ */
+final class NationalCloud
+{
+    const GLOBAL = "https://graph.microsoft.com";
+    const US_GOV = "https://graph.microsoft.us";
+    const US_DOD = "https://dod-graph.microsoft.us";
+    const GERMANY = "https://graph.microsoft.de";
+    const CHINA = "https://microsoftgraph.chinacloudapi.cn";
+
+    /**
+     * Stores all enum values as list
+     * Prevents having to do reflection for each call to getValues()
+     *
+     * @var array
+     */
+    private static $values = [];
+
+    /**
+     * Returns a list of the constant values
+     *
+     * @return array
+     */
+    public static function getValues(): array {
+        if (!self::$values) {
+            $reflectedClass = new \ReflectionClass(__CLASS__);
+            self::$values = array_values($reflectedClass->getConstants());
+        }
+        return self::$values;
+    }
+}

src/Exception/ClientInitialisationException.php

@@ -0,0 +1,10 @@
+<?php
+
+
+namespace Microsoft\Graph\Exception;
+
+
+class ClientInitialisationException extends GraphException
+{
+
+}